1. Field of the Invention
The present invention relates to a rubber modified polystyrene composition having excellent environmental stress-crack resistance (ESCR) properties, and more specifically, it relates to a flon-resistant rubber modified polystyrene composition.
2. Description of the Prior Art
In general, rubber modified polystyrenes are moldable and have excellent physical properties, and are therefore suitable for use in various applications. However, conventional rubber modified polystyrenes have poor resistance to flon compounds (i.e., fluorocarbons) or oils, and for this reason, they tend to develop environmental stress cracks and other problems after being used only a short period of time.
Various rubber modified polystyrenes which have environmental stress-crack resistance properties when exposed to long chain oils or a fats have been studied, as described in Japanese PCT Patent Application Laid-Open No. 504450/1996 and Japanese Patent Application Laid-Open No. 12845/1996. These documents describe the oil resistance of rubber modified polystyrenes used in margarine containers, trays for a refrigerators, and the like. However, these documents do not describe polystyrenes having satisfactory flon-resistance properties.
When rubber modified polystyrenes are used as refrigerator liners, the physical properties of the polystyrene are noticeably impaired by the residual flon compounds used as foaming agents in the polyurethane foam which contacts the liner. Contact with these residual flon compounds causing cracking to occur in the polystyrene. In order to prevent such cracking, it is necessary to provide a flon-resistant material between the liner and the polyurethane, or to employ an expensive material such as an ABS resin which has flon-resistant properties. It is therefore desirable to develop a rubber modified polystyrene which itself has flon-resistant properties.